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U-Boat – the Great War

The U-boats were succeeding beyond all expectations, for the first three months of the new campaign can only be described as a massacre. Henning von Holtzendorff’s target figure of 600,000 tons sunk per month was still valid, and now the German Navy had even more U-boats available —over 130—with which to mount the offensive. That first month, February, the German submarines sank 520,000 tons, very close to their target figure; the next month they did even better at 564,000 tons. But in April the figure soared to 860,000 tons, a figure that crippled the British shipping industry in a matter of months and in so doing strangled the British economy even more thoroughly than the British blockade had throttled Germany’s.

One key to the U-boats’ success, to which the British had no counter, was the sheer ruthlessness of the German attack. Victims in the first three months of the new U-boat offensive included ships flying the flags not only of all of the Allied powers, but also the ensigns of the United States, Sweden, Denmark, the Netherlands, Brazil, Spain, and Norway. The magnitude of the threat was so great and the likelihood of being attacked so real that many skippers refused to take their ships to British ports—and those already in British ports refused to sail, 600 neutral-flagged ships doing so in February alone.

Abetting the German U-boat commanders’ determination to press home their attacks was the Royal Navy’s inability to adequately defend the merchant ships sailing into and out of British ports and harbors. This was not due to any lack of willingness on the navy’s part, but rather from something far more basic—a lack of ships. The submarine’s natural enemy was the destroyer, which had the speed, firepower, and agility to handily dispatch an attacking submarine, the mongoose to the U-boat’s cobra. But the Royal Navy’s destroyer forces were simply stretched too thin. There were three missions with which the destroyers were tasked: securing the Channel crossings to France, screening the Grand Fleet when it sailed from Scapa, and protecting merchant shipping sailing to and from the British Isles. In the spring of 1917 the Royal Navy possessed 260 destroyers of all types, many of them of prewar construction and showing their age. One hundred of them were at any given time assigned to screening duties with the Grand Fleet, the balance being parceled out to the remaining commands to the best of the Admiralty’s ability.

The problem was that just as geography had crippled the High Seas Fleet by bottling it up in the North Sea, so geography aided the U-boats in their hunt for merchant shipping. There were only two passages to the British Isles, together called the Western Approaches. One lies above Ireland and leads past Belfast into the northern mouth of the Irish Channel, giving access to Glasgow, the Tyne, and Liverpool. The other lies to the south, in the waters of the Irish Sea and the Bay of Biscay, opening into the southern end of the Irish Channel, as well as the English Channel and ultimately the mouth of the Thames. Liverpool, Bristol, Southampton, and London were all accessible from this southern route. But these restricted waters had a funnel-like effect on merchant ships, essentially forcing them into areas where the U-boats knew they would find them. It was not difficult; in fact, the U-boats would have had to work at not stumbling across their targets: each month more than 5,000 merchant ships entered or departed British ports and harbors.

For the British destroyers, the problem was exactly the opposite: their numbers were too few, and they were attempting to hunt down opponents who were relatively few in number as well. Unless a destroyer happened to be in the immediate vicinity when a U-boat struck, there was little the British ships could do but resort to endless patrolling in the hope of forcing any U-boats in the area to depart for safer waters, and look to luck in spotting a U-boat careless enough to be cruising on the surface. The submarines, on the other hand, had the luxury of being able to pick their location, and simply wait for their targets to appear, which, given the number of ships passing in and out of British waters, was inevitable.

In December 1916, John Jellicoe passed command of the Grand Fleet to David Beatty when he was called to London to assume the duties of First Sea Lord, and with them came the responsibility for defending against the U-boats. On December 18, 1916, he created a new department, the Anti- Submarine Division, and gave it to Rear Admiral Alexander Duff. Duff was energetic and imaginative, and immediately set about increasing the number of armed merchantmen, laying additional defensive minefields, laying out new protected routes for merchantmen to follow in British waters—and changing them frequently to confuse the U-boats—and assigning destroyer and trawler patrols to those routes. Yet despite his best efforts the rate of sinkings increased. On February 21, 1917, Jellicoe informed the First Lord and the Cabinet that, in his words, “The position is exceedingly grave.” Before long the government would have to face the question of “how long can we continue to carry on the war if the losses of merchant shipping continue at the present rate.”

The answer was not long in coming—by early April not long after the United States declared war on Germany, Jellicoe confided to Admiral William S. Sims, the newly appointed American naval liaison officer in London, that there was less than a six-weeks’ supply of grain in Great Britain, and that unless something were done to stop the hemorrhaging, the U-boats were about to bleed the country dry. According to Jellicoe’s figures, even with the most stringent rationing and conservation measures, if the destruction of Britain’s merchant fleet continued at its present pace, it would be impossible for Great Britain to hold out beyond November 1.

Sims was, in his words, “fairly astounded.” He confessed to Jellicoe that neither he nor anyone in the United States realized that the situation had become so grave. Seeking the British Admiral’s advice, he then sent a long, detailed cable to the Navy Department in Washington, DC, describing in uncompromising terms the conditions in Britain. He asked for every available destroyer and light cruiser to be sent to assist the Royal Navy, characterizing the urgency as being “one of life or death.”

There was, to Sims, one obvious solution to the problem: convoy. It was not a new idea to the Royal Navy: it had been forming and escorting convoys since the middle of the eighteenth century. It had experienced considerable success with convoys during the Great War, particularly in the opening days when the whole of the British Expeditionary Force was carried across the Channel to France without losing a single soldier—a practice that continued throughout the war. Troopships regularly traveled in convoy throughout the Mediterranean, and convoys had carried all the troops to and from Gallipoli without a loss. And yet, as late as January 1917, the Admiralty was still advocating that merchant ships make their sailings alone—with near-catastrophic results.

This was not, though popular belief came to hold it so, because the Admiralty lacked imagination or was too conservative, too blind, or too backward in its thinking to see the wisdom of adopting a convoy system for merchant shipping. The primary reason that convoys were not begun was a lack of escorts.

There were two specific advantages convoy bestowed on the defending forces. First, it reduced the number of opportunities any given submarine had to encounter a target—a convoy of 20 ships presented only a single chance for a U-boat to make its attack, while the same 20 ships sailing independently offered 20 separate opportunities for attack. Second, because the ships were concentrated in a relatively small area, it was possible to concentrate the escorts with them, rather than have them spread out across vast expanses of ocean, dramatically increasing their effectiveness by placing them at the spot where a U-boat attack was likely, exposing the submarines to greatly increased risk of counterattack and destruction.

The Admiralty knew all of this. What held Whitehall back from beginning convoys as soon as the Germans resumed unrestricted submarine warfare was their belief that convoys were beyond the abilities of civilian merchant ships and crews to maintain. The trooping convoys across the Channel and in the Mediterranean were made up of ships, usually commandeered passenger liners, that were commanded by officers of the Royal Navy or the Royal Naval Reserve and manned by reservist crews with a leavening of regulars. These were men with the training and experience in the precise navigation and shiphandling required for convoy work. Civilian merchantmen, on the other hand, were accustomed to following whatever courses and speeds they chose, and their navigation was often haphazard and sloppy, while the concept of steaming in formation, vital to the success of a convoy, was an utterly alien concept to most merchant skippers. In the opinion of the Royal Navy, given these circumstances convoys would be impossible to form or maintain.

This was not, as it might appear, simply a case of Royal Navy prejudice against the merchant marine. These conclusions were based on conferences in late February 1917 with merchant captains who offered these conclusions as their professional opinions based on decades of experience. Nor was it a case of reverse prejudice on the part of the merchant marine: if anything, the merchant officers and crews wanted to find some protection from the marauding U-boats as much if not more than did the Royal Navy. But the facts were blunt: in the first three months of Germany’s new U-boat campaign almost 2 million tons of shipping were destroyed—at a cost to the Imperial German Navy of seven U-boats sunk. It seemed that introducing convoys for all merchant ships sailing to or from the British Isles was the only alternative.

Rear Admiral Duff took it upon himself to determine once and for all whether convoys actually provided more protection for the merchantmen. Combining all of the facts accumulated from three years of experience with convoys along with the three separate U-boat campaigns of 1915, 1916, and 1917, Duff drew up a highly detailed, carefully thought-out memorandum recommending the introduction of a convoy system. The objections of the merchant marine were noted and ruthlessly overridden: the civilian officers and crew simply had to learn the new skills convoy required. The scarcity of escorts would be overcome by the arrival of American destroyers, some of which were already on their way across the Atlantic. Duff immediately went to Jellicoe on April 23 to make his case. Jellicoe in turn instantly saw the validity of Duff’s work and conclusions, circulated the memo to the Admiralty on April 25, and two days later gave his approval to the formation of the first convoys.

The results were almost instantaneous. On May 10 a convoy of 16 merchant ships accompanied by five escorts left Gibraltar for Plymouth. They arrived intact on May 20, necessity and peril being excellent teachers, the merchant crews having learned that the skills needed to keep station and follow zigzagging courses were not beyond them. The first transatlantic convoy soon followed: 12 merchantmen left Hampton Roads, Virginia, for Bristol on May 24. Two stragglers fell out, one of which was later torpedoed and sunk, while the remaining ten reached Bristol under the watchful eyes of eight destroyers. No German submarine had dared to attack them.

By the end of July the rate of sinkings dropped from 25 percent of all ships sailing to the British Isles to one-tenth of that figure, and this despite a dramatic rise in the number of ships sailing from American to Great Britain; of 354 ships crossing the Atlantic, just two were lost to U-boats.

Churchill later summed up the how and why of the convoys’ sudden success:

The size of the sea is so vast that the difference between the size of a convoy and the size of a single ship shrinks in comparison almost to insignificance. There was in fact very nearly as good a chance of a convoy of forty ships in close order slipping unperceived between the patrolling U-boats as there was for a single ship; and each time this happened, forty ships escaped instead of one.

Even better, from the Royal Navy’s perspective, was that by keeping the escorts close to the U-boats’ intended targets, they created more opportunities for attacking the enemy submarines. The U-boat would be irresistibly drawn to the convoy, where the destroyers and trawlers waited to pounce on it; this was a new form of offensive warfare, one that set previous thinking on its ear. For three years the Royal Navy had been trying to take the war to the U-boats, now the convoys brought the U-boats to them. The British did not have to go looking for the Germans, they came as if by invitation. Even if the submarine were not sunk, if it were prevented from making its attacks, that counted as a success.